The present invention relates to a process for preparing polyurea-polyurethane elastomers comprising reacting in a closed mold, in accordance with the reaction injection molding technique, an isocyanate prepolymer having an isocyanate content of about 5 wt. % to 10 wt. % and a molecular weight range of about 1000 to 4000 with a diamine chain extender having no isocyanate-reactive groups other than amino groups in the substantial absence of compounds having isocyanate-reactive groups other than amino groups. The present invention further relates to the polyurea-polyurethane elastomers produced by the process of this invention.
The preparation of elastomers from isocyanate-terminated prepolymers and aromatic amine chain extenders using a casting technique has been described. E.g., U.S. Pat. No. 3,428,610. Such reactions of prepolymers and amines, in which no hydroxyl-group-containing compounds are present after formation of the prepolymer, have not been considered suitable for the reaction injection molding ("RIM") process. Use of the RIM process for the preparation of elastomeric products from a reaction mixture of an isocyanate, a polyhydroxyl compound, and an aromatic amine has been described. E.g., U.S. Pat. No. 4,218,543. When using amine chain extenders in RIM processes, however, at least a portion of the hydroxyl-group-containing compound has heretofore been added along with the amine and, if the isocyanate is a prepolymer, after the formation of prepolymer component is completed.
The use of isocyanate-terminated prepolymers in combination with the same types of amines as described in U.S. Pat. Nos. 3,428,610 and 4,218,543 in a RIM process is also broadly described in the patent literature. See, e.g., U.S. Pat. Nos. 4,296,212, 4,297,444, 4,321,333, and 4,374,210. The use of polyesters in a RIM process is broadly described in U.S. Pat. Nos. 4,590,219 and 4,341,875, while the use of polyester-based prepolymers in a RIM process is broadly described in U.S. Pat. Nos. 4,296,212, 4,297,444, and 4,374,210. U.S. application Ser. No. 238,436, filed on Aug. 30, 1988, describes the use of a neopentyl adipate based prepolymer in a RIM process. Prepolymers and quasi-prepolymers used in the RIM process typically have an NCO content of at least 10% by weight and generally 20% to 40% by weight. See, e.g., U.S. Pat. Nos. 4,631,298 and 4,324,867. None of the above references discloses a process in which a true prepolymer having an isocyanate content of less than about 10% reacts with diamine chain extenders under RIM conditions in the absence of hydroxyl-group-containing compounds. It has now surprisingly been found that prepolymers having an NCO content of only about 4% to about 10% by weight can be used advantageously in a RIM process using diamine chain extenders in the absence of hydroxyl-group-containing compounds.